Systems and methods for improving channel estimation

ABSTRACT

A method for improving channel estimation in a wireless communication system is disclosed. A wireless signal that includes a plurality of multipath components is received. N channel estimates are then obtained, where N is any positive integer greater than one. Each channel estimate of the N channel estimates corresponds to a different multipath component of the plurality of multipath components. The effects of interference between the plurality of multipath components on the N channel estimates is then reduced.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent is a Continuation and claims priorityto patent application Ser. No. 10/368,765 entitled “Systems and Methodsfor Improving Channel Estimation” filed Feb. 18, 2003, now allowed, andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

REFERENCE TO CO-PENDING APPLICATIONS FOR PATENT

The present Application for Patent is related to the followingco-pending U.S. Patent Applications:

“Communication Receiver with an Adaptive Equalizer” by Yongbin Wei,Durga Malladi, and Josef Blanz, having U.S. Ser. No. 10/368,920, filedFeb. 18, 2003, assigned to the assignee hereof, and expresslyincorporated by reference herein;

“Communication Receiver with an Adaptive Equalizer Length” by DurgaMalladi, Josef Blanz and Yongbin Wei, having U.S. Ser. No. 10/369,287,filed Feb. 18, 2003, assigned to the assignee hereof, and expresslyincorporated by reference herein;

“Communication Receiver with an Adaptive Equalizer That Uses ChannelEstimation” by Durga Malladi, Josef Blanz and Yongbin Wei, having U.S.Ser. No. 10/368,891, Feb. 18, 2003, assigned to the assignee hereof, andexpressly incorporated by reference herein.

“Communication Receiver with an Adaptive Equalizer and a Rake ReceiverWith Channel Estimation” by Durga Malladi, Josef Blanz and Yongbin Wei,having U.S. Ser. No. 10/368,892, filed Feb. 18, 2003, assigned to theassignee hereof, and expressly incorporated by reference herein.

BACKGROUND

1. Field

The present invention relates generally to channel estimation incommunications systems, and more specifically, to systems and methodsfor improving channel estimation in wireless communication systems.

2. Background

Communications systems are used for transmission of information from onedevice to another. Prior to transmission, information is encoded into aformat suitable for transmission over a communication channel. Awireless signal containing the encoded information is then transmittedover the communication channel. A communication receiver is used toreceive the wireless signal.

Typically, the received wireless signal includes a plurality ofmultipath components. These multipath components are different versionsof the wireless signal that are generated by reflections from structuresand natural formations. The different multipath components experiencedegradation from noise as they travel through the communication channel.Thus, each multipath component includes a signal component thatcorresponds to the transmitted signal and a noise component that doesnot correspond to the transmitted signal.

Sometimes, a channel estimate is used in a communication receiver.Interference between the multipath components of a wireless signal maymake it difficult to obtain an accurate channel estimate. A need exists,therefore, for an improved channel estimation technique in which theeffects of multipath interference are minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a spread spectrum communication system thatsupports a number of users;

FIG. 2 is a block diagram of a base station and a mobile station in acommunications system;

FIG. 3 is a block diagram illustrating the downlink and the uplinkbetween the base station and the mobile station;

FIG. 4 is a block diagram of the channels in an embodiment of thedownlink;

FIG. 5 is a block diagram of the channels in an embodiment of theuplink;

FIG. 6 is a block diagram of an embodiment of a subscriber unit;

FIG. 7 is a functional block diagram illustrating the transmission of awireless signal;

FIG. 8 is a functional block diagram illustrating the reception of awireless signal;

FIG. 9 is a functional block diagram of an embodiment of the enhancedchannel estimator; and

FIG. 10 is a flow diagram illustrating an embodiment of a method forimproving channel estimation in a wireless communication system.

DETAILED DESCRIPTION

The word “exemplary” is used exclusively herein to mean “serving as anexample, instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. While the various aspects of theembodiments are presented in drawings, the drawings are not necessarilydrawn to scale unless specifically indicated.

The following discussion develops the exemplary embodiments of thesystems and methods for improving channel estimation by first discussinga spread-spectrum wireless communication system. A base station and amobile station, as well as the communications sent therebetween, arethen discussed. The components of an embodiment of a subscriber unit arethen shown. Functional block diagrams are shown and described inrelation to the transmission and reception of a wireless signal. Detailsregarding an enhanced channel estimator are also set forth. An exemplarymethod for improving channel estimation in a wireless communicationsystem is then discussed.

Note that the exemplary embodiment is provided as an exemplar throughoutthis discussion; however, alternate embodiments may incorporate variousaspects without departing from the scope of the present invention.Specifically, the present invention is applicable to a data processingsystem, a wireless communication system, a mobile IP network and anyother system desiring to receive and process a wireless signal.

The exemplary embodiment employs a spread-spectrum wirelesscommunication system. Wireless communication systems are widely deployedto provide various types of communication such as voice, data, and soon. These systems may be based on code division multiple access (CDMA),time division multiple access (TDMA), or some other modulationtechniques. A CDMA system provides certain advantages over other typesof systems, including increased system capacity.

A system may be designed to support one or more standards such as the“TIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standard forDual-Mode Wideband Spread Spectrum Cellular System” referred to hereinas the IS-95 standard, the standard offered by a consortium named “3rdGeneration Partnership Project” referred to herein as 3GPP, and embodiedin a set of documents including Document Nos. 3GPP TS 25.211, 3GPP TS25.212, 3GPP TS 25.213, and 3GPP TS 25.214, 3GPP TS 25.302, referred toherein as the W-CDMA standard, the standard offered by a consortiumnamed “3rd Generation Partnership Project 2” referred to herein as3GPP2, and TR-45.5 referred to herein as the cdma2000 standard, formerlycalled IS-2000 MC. The standards cited hereinabove are hereby expresslyincorporated herein by reference.

Each standard specifically defines the processing of data fortransmission from base station to mobile station, and vice versa. As anexemplary embodiment the following discussion considers aspread-spectrum communication system consistent with the cdma2000standard of protocols. Alternate embodiments may incorporate anotherstandard.

The systems and methods described herein may be used with high data ratecommunication systems. Throughout the following discussion a specifichigh data rate system is described for clarity. Alternate systems may beimplemented that provide transmission of information at high data rates.For CDMA communications systems designed to transmit at higher datarates, such as a High Data Rate (HDR) communications system, a variabledata rate request scheme may be used to communicate at the maximum datarate that the carrier-to-interference ratio (C/I) may support. The HDRcommunications system is typically designed to conform to one or morestandards such as the “cdma2000 High Rate Packet Data Air InterfaceSpecification,” 3GPP2 C.S0024, Version 2, Oct. 27, 2000, promulgated bythe consortium “3^(rd) Generation Partnership Project 2.” The contentsof the aforementioned standard is incorporated by reference herein.

A receiver in an exemplary HDR communications system may employ avariable rate data request scheme. The receiver may be embodied in asubscriber station in communication with a land-based data network bytransmitting data on an uplink to a base station (shown below). The basestation receives the data and routes the data through a base stationcontroller (BSC) (not shown) to the land-based network. Conversely,communications to the subscriber station may be routed from theland-based network to the base station via the BSC and transmitted fromthe base station to the subscriber unit on a downlink.

FIG. 1 serves as an example of a communications system 100 that supportsa number of users and is capable of implementing at least some aspectsof the embodiments discussed herein. Any of a variety of algorithms andmethods may be used to schedule transmissions in system 100. System 100provides communication for a number of cells 102A-102G, each of which isserviced by a corresponding base station 104A-104G, respectively. In theexemplary embodiment, some of the base stations 104 have multiplereceive antennas and others have only one receive antenna. Similarly,some of the base stations 104 have multiple transmit antennas, andothers have single transmit antennas. There are no restrictions on thecombinations of transmit antennas and receive antennas. Therefore, it ispossible for a base station 104 to have multiple transmit antennas and asingle receive antenna, or to have multiple receive antennas and asingle transmit antenna, or to have both single or multiple transmit andreceive antennas.

Terminals 106 in the coverage area may be fixed (i.e., stationary) ormobile. As shown in FIG. 1, various terminals 106 are dispersedthroughout the system. Each terminal 106 communicates with at least oneand possibly more base stations 104 on the downlink and uplink at anygiven moment depending on, for example, whether soft handoff is employedor whether the terminal is designed and operated to (concurrently orsequentially) receive multiple transmissions from multiple basestations. Soft handoff in CDMA communications systems is well known inthe art and is described in detail in U.S. Pat. No. 5,101,501, entitled“Method and System for Providing a Soft Handoff in a CDMA CellularTelephone System”, which is assigned to the assignee of the presentinvention.

The downlink refers to transmission from the base station 104 to theterminal 106, and the uplink refers to transmission from the terminal106 to the base station 104. In the exemplary embodiment, some ofterminals 106 have multiple receive antennas and others have only onereceive antenna. In FIG. 1, base station 104A transmits data toterminals 106A and 106J on the downlink, base station 104B transmitsdata to terminals 106B and 106J, base station 104C transmits data toterminal 106C, and so on.

FIG. 2 is a block diagram of the base station 202 and mobile station 204in a communications system 100. The base station 202 is in wirelesscommunication with the mobile station 204. As mentioned above, the basestation 202 transmits signals to mobile stations 204 that receive thesignals. In addition, mobile stations 204 may also transmit signals tothe base station 202.

FIG. 3 is a block diagram of the base station 202 and mobile station 204illustrating the downlink 302 and the uplink 304. The downlink 302refers to transmissions from the base station 202 to the mobile station204, and the uplink 304 refers to transmissions from the mobile station204 to the base station 202.

FIG. 4 is a block diagram of the channels in an embodiment of thedownlink 302. The downlink 302 includes the pilot channel 402, the syncchannel 404, the paging channel 406 and the traffic channel 408. Thedownlink 302 illustrated is only one possible embodiment of a downlink302 and it will be appreciated that other channels may be added orremoved from the downlink 302.

Under one CDMA standard, described in the Telecommunications IndustryAssociation's TIA/EIA/IS-95-A Mobile Stations-Base Station CompatibilityStandard for Dual-Mode Wideband Spread Spectrum Cellular System, eachbase station 202 transmits pilot 402, sync 404, paging 406 and forwardtraffic 408 channels to its users. The pilot channel 402 is anunmodulated, direct-sequence spread spectrum signal transmittedcontinuously by each base station 202. The pilot channel 402 allows eachuser to acquire the timing of the channels transmitted by the basestation 202, and provides a phase reference for coherent demodulation.The pilot channel 402 also provides a means for signal strengthcomparisons between base stations 202 to determine when to hand offbetween base stations 202 (such as when moving between cells 102).

The sync channel 404 conveys timing and system configuration informationto the mobile station 204. The paging channel 406 is used to communicatewith mobile stations 204 when they are not assigned to a traffic channel408. The paging channel 406 is used to convey pages, that is,notifications of incoming calls, to the mobile stations 204. The trafficchannel 408 is used to transmit user data and voice. Signaling messagesare also sent over the traffic channel 408.

FIG. 5 is a block diagram of the channels in an embodiment of the uplink304.

The uplink 304 may include a pilot channel 502, an access channel 504and a traffic channel 506. The uplink 304 illustrated is only onepossible embodiment of an uplink and it will be appreciated that otherchannels may be added or removed from the uplink 304.

The uplink 304 of FIG. 5 includes a pilot channel 502. Recall thatthird-generation (3G) wireless radiotelephone communication systems havebeen proposed in which an uplink 304 pilot channel 502 is used. Forexample, in the currently proposed cdma2000 standard, the mobile station204 transmits a Reverse Link Pilot Channel (R-PICH) that the basestation 202 uses for initial acquisition, time tracking, rake-receivercoherent reference recovery, and power control measurements. Thus,systems and methods herein are applicable to pilot signals on thedownlink 302 and on the uplink 304.

The access channel 504 is used by the mobile station 204 to communicatewith the base station 202 when the mobile 204 does not have a trafficchannel 506 assigned. The uplink traffic channel 506 is used to transmituser data and voice. Signaling messages are also sent over the uplinktraffic channel 506.

An embodiment of a mobile station 204 is shown in a subscriber unitsystem 600 illustrated in the functional block diagram of FIG. 6. Thesystem 600 includes a processor 602 which controls operation of thesystem 600. The processor 602 may also be referred to as a CPU. Memory604, which may include both read-only memory (ROM) and random accessmemory (RAM), provides instructions and data to the processor 602. Aportion of the memory 604 may also include non-volatile random accessmemory (NVRAM).

The system 600, which is typically embodied in a wireless communicationdevice such as a cellular telephone, also includes a housing 606 thatcontains a transmitter 608 and a receiver 610 to allow transmission andreception of data, such as audio communications, between the system 600and a remote location, such as a cell site controller or base station202. The transmitter 608 and receiver 610 may be combined into atransceiver 612. An antenna 614 is attached to the housing 606 andelectrically coupled to the transceiver 612. Additional antennas (notshown) may also be used. The operation of the transmitter 608, receiver610 and antenna 614 is well known in the art and need not be describedherein.

The system 600 also includes a signal detector 616 used to detect andquantify the level of signals received by the transceiver 612. Thesignal detector 616 detects such signals as total energy, pilot energyper pseudonoise (PN) chips, power spectral density, and other signals,as is known in the art.

A state changer 626 of the system 600 controls the state of the wirelesscommunication device based on a current state and additional signalsreceived by the transceiver 612 and detected by the signal detector 616.The wireless communication device is capable of operating in any one ofa number of states.

The system 600 also includes a system determinator 628 used to controlthe wireless communication device and determine which service providersystem the wireless communication device should transfer to when itdetermines the current service provider system is inadequate.

The various components of the system 600 are coupled together by a bussystem 630 which may include a power bus, a control signal bus, and astatus signal bus in addition to a data bus. However, for the sake ofclarity, the various busses are illustrated in FIG. 6 as the bus system630. The system 600 may also include a digital signal processor (DSP)607 for use in processing signals. One skilled in the art willappreciate that the system 600 illustrated in FIG. 6 is a functionalblock diagram rather than a listing of specific components.

The methods disclosed herein may be implemented in an embodiment of asubscriber unit 600. The disclosed systems and methods may also beimplemented in other communication systems with a receiver, such as abase station 202. If a base station 202 is being used to implement thedisclosed systems and methods, the functional block diagram of FIG. 6may also be used to describe components in a functional block diagram ofa base station 202.

FIG. 7 is a functional block diagram illustrating the transmission of awireless signal. The functional block diagram of FIG. 7 may beimplemented in various components, such as the base station 202 and themobile station 204.

As shown, the wireless signal includes a pilot channel 702 and otherorthogonal channels 704. Additional non-orthogonal channels 706 may alsobe included in the wireless signal. Examples of non-orthogonal channelsinclude the synchronization channel (SCH), channels scrambled by thesecondary scrambling code (SSC) in WCDMA, and channels spread byquasi-orthogonal sequences (QOS) in cdma2000.

The orthogonal channels are provided to an orthogonal spreadingcomponent 708. Both the orthogonal and non-orthogonal channels are thenprovided to a channel gain component 710, which adds a gain for thechannel. The outputs from the channel gain components 710 are summedtogether as shown by the summer 712. As shown in FIG. 7, thenon-orthogonal channels may be time-division multiplexed (TDM) 711. Inother embodiments, one or more of the orthogonal channels may betime-division multiplexed.

The non-orthogonal channels 706 do not have orthogonal spreadingcomponents. Some non-orthogonal channels 706 (e.g., the synchronizationchannel) may be fed directly into a channel gain component 710. Othernon-orthogonal channels 706 (e.g., channels spread by quasi-orthogonalsequences in cdma2000) are spread in a non-orthogonal way and then fedinto a channel gain component 710. The outputs of the channel gaincomponents 710 are summed with the summer 712.

The summed signal is fed into the pseudorandom noise (PN) scramblingcomponent 714. A baseband filter 716 takes the output from the PNscrambling component 714 and provides the filtered output 716 to atransmitter 718. The transmitter 718 includes an antenna 720. Thetransmitted signal 721 then enters the radio channel 722.

FIG. 8 is a functional block diagram illustrating the reception of awireless signal 801. A receiver 802 receives the wireless signal 801through the use of an antenna 804. The received wireless signal 801includes a plurality of multipath components. Each multipath componentincludes a signal component that corresponds to the transmitted signal721 and a noise component that does not correspond to the transmittedsignal 721.

The received wireless signal 801 is provided to a matched filter 805that is matched to the impulse response of the baseband filter 716. Theoutput 806 of the matched filter 805 is provided to an enhanced channelestimator 808. The enhanced channel estimator 808 calculates a pluralityof enhanced channel estimates 810. Each of the enhanced channelestimates 810 corresponds to a different multipath component within thereceived wireless signal 801. The enhanced channel estimates 810 areenhanced with respect to channel estimates calculated using knowntechniques. In particular, the enhanced channel estimates 810 arecalculated so as to minimize the effects of interference between theplurality of multipath components (multipath interference). Anembodiment of the enhanced channel estimator 808 will be describedbelow.

The enhanced channel estimates 810 are then provided to a furtherprocessing component 812 for further processing. In one embodiment, theenhanced channel estimates 810 are used in an equalizer. In anotherembodiment, the enhanced channel estimates 810 are used in a rakereceiver.

FIG. 9 is a block diagram illustrating logical components within anembodiment of the enhanced channel estimator 908. The enhanced channelestimator 908 includes a delay estimator 902. The delay estimator 902estimates N delays 904, where N is any positive integer greater thanone. Each of the N delays 904 corresponds to a different multipathcomponent within the received wireless signal 801.

As described above, the systems and methods disclosed herein may beimplemented in a wireless communication system that utilizes CDMAtechniques. In such a wireless communication system, each multipathcomponent within the received wireless signal 801 includes a pluralityof chips. Each chip spans a certain time duration defined by the chiprate. In some embodiments, at least some of the multipath componentswithin the received wireless signal 801 are separated from one anotherby less than the chip duration. In such embodiments, at least some ofthe N delays 904 are also separated from one another by less than thechip duration.

The enhanced channel estimator 908 also includes N PN descramblers 906that perform PN descrambling on the output 806 of the matched filter805. Thus, PN descrambling is performed N times on the output 806 of thematched filter 805, and N descrambled signals 912 are obtained. Each PNdescrambler 906 aligns the signal and the descrambling sequence based onthe delay 904 prior to conducting descrambling.

The enhanced channel estimator 808 also includes a plurality ofcorrelators 914 that correlate one of the N descrambled signals 912 witha reference signal 916 to obtain a channel estimate 918. As shown, Nchannel estimates 918 are obtained. Each channel estimate 918corresponds to a different multipath component within the receivedwireless signal 801. In one embodiment, the reference signal 916 onlyincludes the pilot channel 402. In another embodiment, the referencesignal 916 includes the pilot channel 402 and the traffic channel 408.In another embodiment, the reference signal 916 includes the pilotchannel 402, the traffic channel 408, and an estimate of a ratio betweenthe traffic channel 408 and the pilot channel 402.

The enhanced channel estimator 808 also includes a matrix calculationcomponent 920. The matrix calculation component 920 calculates amultipath correlation matrix 922 and a noise covariance matrix 924. Asmentioned previously, the received wireless signal 801 includes aplurality of multipath components. The multipath correlation matrix 922includes information about how signal components within the plurality ofmultipath components are correlated with one another. The noisecovariance matrix 924 includes information about how noise componentswithin the plurality of multipath components are correlated with oneanother. The N delays 904, the N channel estimates 918, and thereference signal 916 are used to calculate both the multipathcorrelation matrix 922 and the noise covariance matrix 924.

The enhanced channel estimator 808 also includes a multipathinterference reduction component 926. As mentioned previously, themultipath components in the received wireless signal 801 may interferewith one another. The multipath reduction component 926 uses themultipath correlation matrix 922 and the noise covariance matrix 924 toreduce the effects of this multipath interference on the N channelestimates 918. Thus, N enhanced channel estimates 810 are obtained.

Referring to FIGS. 7 through 9, the following provides a mathematicaldescription and background of various mathematical formulas that may beused.

The channel estimates 918 may be written as shown in Formula 1. Theparameter ρ in Formula 1 is the baseband filter 716 auto-correlationfunction.

$\begin{matrix}{{y\lbrack m\rbrack} = {{\sum\limits_{i = 0}^{P - 1}{\alpha_{i} \cdot {\rho\left\lbrack {m - i} \right\rbrack}}} + {{v\lbrack m\rbrack}.}}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

In matrix notation, the channel estimates 918 may be written as shown inFormula 2. The parameter A in Formula 2 is the multipath correlationmatrix 922. The parameter α in Formula 2 is a fading coefficient vector.The parameter v in Formula 2 is a noise vector.y=A·α+v   Formula 2.

In one embodiment, reducing the effects of multipath interference on theN channel estimates 918 involves calculating an estimate of the fadingcoefficient vector. This calculation may be performed by the multipathinterference reduction component 926. An estimate of the fadingcoefficient vector may be written as shown in Formula 3. The parameter Ain Formula 3 is the multipath correlation matrix 922. The parameter Λ inFormula 3 is the noise covariance matrix 924.β=[A ^(H)·Λ⁻¹ ·A] ⁻¹ ·A ^(H)·Λ⁻¹ ·y   Formula 3.

FIG. 10 is a flow diagram of a method 1000 for improving channelestimation in a wireless communication system. The method 1000 begins1002 when a wireless signal 801 is received 1004. As mentionedpreviously, the wireless signal 801 includes a plurality of multipathcomponents. Each multipath component includes a signal component thatcorresponds to the transmitted signal 721 and a noise component thatdoes not correspond to the transmitted signal 721.

The received wireless signal 801 is then filtered 1006 using a matchedfilter 805 that is matched to the impulse response of the basebandfilter 716. The method 1000 then involves estimating 1008 N delays 904,where N is any positive integer. Each of the N delays 904 corresponds toa different multipath component within the received wireless signal 801.PN descrambling is then performed 1010 N times on the output 806 of thematched filter 805, once after each of the different delays 904estimated in step 1008. Thus, N descrambled signals 912 are obtained.

Each of the N descrambled signals 912 is then correlated 1012 with areference signal 916 to obtain N channel estimates 918. Each of the Nchannel estimates 918 corresponds to a different multipath componentwithin the received signal 801.

The method 1000 then involves calculating 1014 a multipath correlationmatrix 922 and a noise covariance matrix 924. As mentioned previously,the multipath correlation matrix 922 includes information about howsignal components within the plurality of multipath components arecorrelated with one another. The noise covariance matrix 924 includesinformation about how noise components within the plurality of multipathcomponents are correlated with one another. The N delays 904, the Nchannel estimates 918, and the reference signal 916 are used tocalculate the multipath correlation matrix 922 and the noise covariancematrix 924.

As mentioned previously, the multipath components in the receivedwireless signal 801 may interfere with one another. The multipathcorrelation matrix 922 and the noise covariance matrix 924 are then usedto reduce 1016 the effects of this multipath interference on the Nchannel estimates 918. Thus, N enhanced channel estimates 810 areobtained. The N enhanced channel estimates 810 may be used for furtherprocessing 1018, and the method 1000 may then end 1020.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array signal (FPGA) or other programmable logicdevice, discrete gate or transistor logic, discrete hardware components,or any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processormay read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of thepresent invention. In other words, unless a specific order of steps oractions is required for proper operation of the embodiment, the orderand/or use of specific steps and/or actions may be modified withoutdeparting from the scope of the present invention.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for improving channel estimation in awireless communication system, comprising: receiving a wireless signalthat comprises a plurality of multipath components; estimating a timedelay for at least one of the plurality of multipath components;obtaining N channel estimates, wherein N is any positive integer greaterthan one, wherein each channel estimate of the N channel estimatescorresponds to a different multipath component of the plurality ofmultipath components; and reducing the effects of interference betweenthe plurality of multipath components on the N channel estimates bycalculating and applying a fading coefficient vector estimate to the Nchannel estimates based on a correlation matrix and a covariance matrix;wherein obtaining the N channel estimates comprises correlating each ofN descrambled signals with a reference signal to obtain the N channelestimates, the reference signal including a downlink channel, andwherein the reference signal is further used to calculate thecorrelation matrix and the covariance matrix and reducing the effects ofinterference employs the correlation matrix and the covariance matrix,and the correlation matrix and covariance matrix employ the referencesignal.
 2. The method as defined in claim 1, wherein reducing theeffects of interference comprises calculating a multipath correlationmatrix which comprises information about how signal components within Nof the plurality of multipath components are correlated with oneanother; and calculating a noise covariance matrix which comprisesinformation about how noise components within N of the plurality ofmultipath components are correlated with one another.
 3. The method asdefined in claim 2, wherein the multipath correlation matrix, the noisecovariance matrix, and the fading coefficient vector estimate are usedto reduce the effects of interference between the plurality of multipathcomponents on the N channel estimates.
 4. The method as defined in claim3, wherein obtaining the N channel estimates further comprises:filtering the received wireless signal using a matched filter that ismatched to the impulse response of a baseband filter; estimating Ndelays, wherein each of the N delays corresponds to a differentmultipath component of the plurality of multipath components; andperforming PN descrambling on the output of the matched filter N times,once after each of the N delays, thereby obtaining N descrambledsignals; wherein each of the N channel estimates corresponds to adifferent multipath component of the plurality of multipath components.5. The method as defined in claim 4, wherein the N delays, the N channelestimates, and the reference signal are used to calculate the multipathcorrelation matrix and the noise covariance matrix.
 6. The method asdefined in claim 1, wherein the wireless communication system utilizescode division multiple access techniques.
 7. The method as defined inclaim 6, wherein each multipath component within the plurality ofmultipath components comprises a plurality of chips, each chip having achip duration, and wherein at least some of the plurality of multipathcomponents are separated from one another by less than the chipduration.
 8. The method as defined in claim 1, wherein the method isimplemented by a mobile station.
 9. The method as defined in claim 1,wherein the method is implemented by a base station.
 10. A mobilestation for use in a wireless communication system, the mobile stationcomprising: at least one antenna for receiving a wireless signal thatcomprises a plurality of multipath components; a receiver in electroniccommunication with the at least one antenna; and an enhanced channelestimator that implements a method comprising: estimating a time delayfor at least one of the plurality of multipath components; obtaining Nchannel estimates, wherein N is any positive integer greater than one,wherein each channel estimate of the N channel estimates corresponds toa different multipath component of the plurality of multipathcomponents; and reducing the effects of interference between theplurality of multipath components on the N channel estimates bycalculating and applying a fading coefficient vector estimate to the Nchannel estimates based on a multipath correlation matrix and a noisecovariance matrix; wherein obtaining the N channel estimates comprisescorrelating each of N descrambled signals with a reference signal toobtain the N channel estimates, the reference signal including adownlink channel, and wherein the reference signal is further used tocalculate the multipath correlation matrix and the noise covariancematrix and reducing the effects of interference is based on thecorrelation matrix and the covariance matrix, and the correlation matrixand covariance matrix are based on the reference signal.
 11. The mobilestation as defined in claim 10, wherein reducing the effects ofinterference comprises: calculating the multipath correlation matrixwhich comprises information about how signal components within N of theplurality of multipath components are correlated with one another; andcalculating the noise covariance matrix which comprises informationabout how noise components within N of the plurality of multipathcomponents are correlated with one another.
 12. The mobile station asdefined in claim 11, wherein the multipath correlation matrix, the noisecovariance matrix, and the fading coefficient vector estimate are usedto reduce the effects of interference between the plurality of multipathcomponents on the N channel estimates.
 13. The mobile station as definedin claim 12, wherein obtaining the N channel estimates furthercomprises: filtering the received wireless signal using a matched filterthat is matched to the impulse response of a baseband filter; estimatingN delays, wherein each of the N delays corresponds to a differentmultipath component of the plurality of multipath components; andperforming PN descrambling on the output of the matched filter N times,once after each of the N delays, thereby obtaining N descrambledsignals; wherein each of the N channel estimates corresponds to adifferent multipath component of the plurality of multipath components.14. The mobile station as defined in claim 13, wherein the N delays, theN channel estimates, and the reference signal are used to calculate themultipath correlation matrix and the noise covariance matrix.
 15. Themobile station as defined in claim 10, wherein the wirelesscommunication system utilizes code division multiple access techniques.16. The mobile station as defined in claim 15, wherein each multipathcomponent within the plurality of multipath components comprises aplurality of chips, each chip having a chip duration, and wherein atleast some of the plurality of multipath components are separated fromone another by less than the chip duration.
 17. An apparatus for use ina wireless communication system, the mobile station comprising: at leastone antenna for receiving a wireless signal that comprises a pluralityof multipath components; a receiver in electronic communication with theat least one antenna; and an enhanced channel estimator that implementsa method comprising: estimating a time delay for at least one of theplurality of multipath components; obtaining N channel estimates,wherein N is any positive integer greater than one, wherein each channelestimate of the N channel estimates corresponds to a different multipathcomponent of the plurality of multipath components; and reducing theeffects of interference between the plurality of multipath components onthe N channel estimates by calculating and applying a fading coefficientvector estimate to the N channel estimates based on a correlation matrixand a covariance matrix; wherein obtaining the N channel estimatescomprises correlating each of N descrambled signals with a referencesignal to obtain the N channel estimates, the reference signal includinga downlink channel, and wherein the reference signal is further used tocalculate the correlation matrix and the covariance matrix and reducingthe effects of interference is based on the correlation matrix and thecovariance matrix, and the correlation matrix and covariance matrix arebased on the reference signal.
 18. The apparatus as defined in claim 17,wherein reducing the effects of interference comprises: calculating amultipath correlation matrix which comprises information about howsignal components within N of the plurality of multipath components arecorrelated with one another; and calculating a noise covariance matrixwhich comprises information about how noise components within N of theplurality of multipath components are correlated with one another. 19.The apparatus as defined in claim 18, wherein the multipath correlationmatrix, the noise covariance matrix, and the fading coefficient vectorestimate are used to reduce the effects of interference between theplurality of multipath components on the N channel estimates.
 20. Theapparatus as defined in claim 19, wherein obtaining the N channelestimates comprises: filtering the received wireless signal using amatched filter that is matched to the impulse response of a basebandfilter; estimating N delays, wherein each of the N delays corresponds toa different multipath component of the plurality of multipathcomponents; and performing PN descrambling on the output of the matchedfilter N times, once after each of the N delays, thereby obtaining Ndescrambled signals; wherein each of the N channel estimates correspondsto a different multipath component of the plurality of multipathcomponents.
 21. The apparatus as defined in claim 20, wherein the Ndelays, the N channel estimates, and the reference signal are used tocalculate the multipath correlation matrix and the noise covariancematrix.
 22. The apparatus as defined in claim 17, wherein the wirelesscommunication system utilizes code division multiple access techniques.23. The apparatus as defined in claim 22, wherein each multipathcomponent within the plurality of multipath components comprises aplurality of chips, each chip having a chip duration, and wherein atleast some of the plurality of multipath components are separated fromone another by less than the chip duration.
 24. The apparatus as definedin claim 17, wherein the apparatus comprises a mobile station.
 25. Theapparatus as defined in claim 17, wherein the apparatus comprises a basestation.
 26. A mobile station for use in a wireless communicationsystem, the mobile station comprising: means for estimating a time delayfor at least one of the plurality of multipath components; means forreceiving a wireless signal that comprises a plurality of multipathcomponents; means for obtaining N channel estimate, wherein N is anypositive integer greater than one, wherein each channel estimate of theN channel estimates corresponds to a different multipath component ofthe plurality of multipath components; and means for reducing theeffects of interference between the plurality of multipath components onthe N channel estimates by calculating and applying a fading coefficientvector estimate to the N channel estimates based on a correlation matrixand a covariance matrix; wherein the means for obtaining the N channelestimates is configured to correlate each of the N descrambled signalswith a reference signal to obtain the N channel estimates, the referencesignal including a downlink channel, and wherein the reference signal isfurther used to calculate the correlation matrix and the covariancematrix and reducing the effects of interference is based on thecorrelation matrix and the covariance matrix, and the correlation matrixand covariance matrix are based on the reference signal.
 27. The mobilestation as defined in claim 26, wherein the means for reducing theeffects of interference comprises: means for calculating a multipathcorrelation matrix which comprises information about how signalcomponents within N of the plurality of multipath components arecorrelated with one another; and means for calculating a noisecovariance matrix which comprises information about how noise componentswithin N of the plurality of multipath components are correlated withone another.
 28. The mobile station as defined in claim 27, wherein themultipath correlation matrix, the noise covariance matrix, and thefading coefficient vector estimate are used to reduce the effects ofinterference between the plurality of multipath components on the Nchannel estimates.
 29. The mobile station as defined in claim 26,wherein the wireless communication system utilizes code divisionmultiple access techniques.
 30. The mobile station as defined in claim29, wherein each multipath component within the plurality of multipathcomponents comprises a plurality of chips, each chip having a chipduration, and wherein at least some of the plurality of multipathcomponents are separated from one another by less than the chipduration.
 31. A non-transitory storage medium readable by a processor,the storage medium encoded with a computer program, the computer programcomprising instructions executable to perform a method for improvingchannel estimation in a wireless communication system, the methodcomprising: receiving a wireless signal that comprises a plurality ofmultipath components; estimating a time delay for at least one of theplurality of multipath components; obtaining N channel estimates,wherein N is any positive integer greater than one, wherein each channelestimate of the N channel estimates corresponds to a different multipathcomponent of the plurality of multipath components; and reducing theeffects of interference between the plurality of multipath components onthe N channel estimates by calculating and applying a fading coefficientvector estimate to the N channel estimates based on a correlation matrixand a covariance matrix; wherein obtaining the N channel estimatescomprises correlating each of the N descrambled signals with a referencesignal to obtain the N channel estimates, the reference signal includinga downlink channel, and wherein the reference signal is further used tocalculate the correlation matrix and the covariance matrix and reducingthe effects of interference is based on the correlation matrix and thecovariance matrix, and the correlation matrix and covariance matrix arebased on the reference signal.